Chlorine and felsic magma evolution: Modeling the behavior of an under-appreciated volatile component

Webster, James D.; Iveson, Alexander A.; Rowe, Michael C.; Webster, Paul M.

doi:10.1016/j.gca.2019.12.002

Cited by 23 publications

(11 citation statements)

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“…Further evidence for limited magmatic chlorine in the YPVF hydrothermal system is based on calculations showing that a mixture of about 0.2-0.4 wt.% magmatic fluid with 99.6-99.8 wt.% meteoric water could account for all the discharged thermal chloride (Fournier, 1989). Magmatic chloride in the YPVF hydrothermal system would be manifested by changes in chloride flux from the YPVF and in the values of δ 37 Cl and Cl/B might result from pressure changes in the magmatic system, which would result in chlorine exsolution from the rhyolitic melt (Carroll, 2005;Metrich & Rutherford, 1992;Webster et al, 2020) followed by breaching of the brittle-ductile transition zone to allow transport of the chlorine-rich fluids from magma and its surrounding into the hydrothermal system (Fournier, 1999;Hurwitz & Lowenstern, 2014).…”

Section: Chlorine Lithium and Boron In Alkaline-chloride Watermentioning

confidence: 99%

The Systematics of Chlorine, Lithium, and Boron andδ³⁷Cl,δ⁷Li, and δ¹¹B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field

Cullen

Hurwitz

Barnes

et al. 2021

Geochem Geophys Geosyst

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Chlorine, lithium, and boron are trace elements in rhyolite but are enriched in groundwater flowing through rhyolite because they tend to partition into the fluid phase during high‐temperature fluid‐rock reactions. We present a large data set of major element and δ37Cl, δ7Li, and δ11B compositions of thermal water and rhyolite from Yellowstone Plateau Volcanic Field (YPVF). The Cl/B, Cl/Li, δ37Cl (−0.2‰ to +0.7‰), and δ11B (−6.2‰ to −5.9‰) values of alkaline‐chloride thermal waters reflect high‐temperature leaching of chlorine, lithium, and boron from rhyolite that has δ37Cl and δ11B values of +0.1‰ to +0.9‰ and −6.3‰ to −6.2‰, respectively. Chlorine and boron are not reactive, but lithium incorporation into hydrothermal alteration minerals results in a large range of Cl/Li, B/Li, and δ7Li (−1.2‰ to +3.8‰) values in thermal waters. The relatively large range in δ7Li values of thermal waters reflects a large range of values in rhyolite. Large volumes of rhyolite must be leached to account for the chloride, lithium and boron fluxes, implying deep groundwater flow through rhyolite flows and tuffs representing Yellowstone's three eruptive cycles (∼2.1 Ma). Lower Cl/B values in acid‐sulfate waters result from preferential partitioning of boron into the vapor phase and enrichment in the near‐surface water condensate. The Cl/B, Cl/Li, δ7Li (−0.3‰ to +2.1‰), and δ11B (−8.0‰ to −8.1‰) values of travertine depositing calcium‐carbonate thermal waters which discharge in the northern and southern YPVF suggest that chlorine, lithium, and boron are derived from Mesozoic siliciclastic sediments which contain detrital material from the underlying metamorphic basement.

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Section: Chlorine Lithium and Boron In Alkaline-chloride Watermentioning

confidence: 99%

The Systematics of Chlorine, Lithium, and Boron andδ³⁷Cl,δ⁷Li, and δ¹¹B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field

Cullen

Hurwitz

Barnes

et al. 2021

Geochem Geophys Geosyst

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“…Our samples are chlorine undersaturated, similar to the majority of felsic melt inclusions globally (Webster et al, 2019). We envision that such chlorine undersaturated melts may, prior to or during eruptions, assimilate ambient low δ 37 Cl magmatic brines that have been formed by previous generations of silicic intrusions within the same, long lived silicic magma mush (Fig.…”

Section: Assimilation Of Magmatic Brinesmentioning

confidence: 67%

“…Indeed, a complicated pre-eruptive volatile history is also reflected by high Cl variability in Icelandic propagating rift and rift rhyolites (50 to 2600 ppm) (Fig. S-2), likely reflecting a combination of fractional crystallisation, partial melting, accumulation of fractional melts from volatile heterogeneous sources as well as episodic exsolution and resorption of magmatic volatile phases, including magmatic brines (Webster et al, 2019; Supplementary Information S-3; Fig. 3a).…”

Section: Origin Of Large δ 37 CL Variability: Sources Versus Processesmentioning

confidence: 99%

“…1b, S-4, S-5). Assimilation of brines has been previously demonstrated to take place in submarine basalts, that may directly assimilate seawater-derived brines (Kendrick et al, 2013), and in silicic melts, where surplus Cl contents have been interpreted as assimilation of hydrosaline fluids of unknown origin (Webster et al, 2019).…”

Section: Assimilation Of Magmatic Brinesmentioning

confidence: 99%

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Chlorine isotope ratios record magmatic brine assimilation during rhyolite genesis

Ranta¹,

Halldórsson²,

Barnes³

et al. 2021

Geochem. Persp. Let.

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Magmatic volatile phases within crustal silicic magma domains influence key volcanic processes such as the build up to eruptions and formation of magmatic-hydrothermal ore deposits. However, the extent and nature of fluid-melt interaction in such environments is poorly understood, as geochemical signals in volcanic rocks originating from pre-eruptive volatile processes are commonly overprinted by syn-eruptive degassing. Here, we use δ 37 Cl as a conservative tracer of brine-melt interaction on a broad suite of silicic volcanic rocks from Iceland. We find that the δ 37 Cl values of silicic rocks are systematically shifted to more negative values compared to associated basalts and intermediate rocks by up to 2.9 ‰. These large shifts cannot be explained by well known processes inherent to silicic magma genesis, including crustal assimilation, mineral-melt fractionation and syn-eruptive degassing. Instead, we show that low δ 37 Cl values in silicic rocks can be attributed to assimilation of magmatic brines that are formed and stored in long lived crustal magma mushes. Our results indicate that magmatic brine assimilation is a fundamental, but previously unrecognised part of rhyolite genesis.

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“…The presence of a MVP is commonly predicted in recently developed models of mush-dominated magma reservoirs (Edmonds and Wallace, 2017;Parmigiani et al, 2017;Degruyter et al, 2019) and is fundamental in controlling differentiation processes and, in some cases, explosivity in magmatic systems (Anderson et al, 1984;Sisson and Bacon, 1999;Pistone et al, 2015;Degruyter et al, 2017;Bachmann and Huber, 2018;Cassidy et al, 2018;Popa et al, 2019). Decades of careful work describing solubilities and H 2 O-CO 2 concentrations in magmas (Tuttle and Bowen, 1958;Burnham and Jahns, 1962;Dingwell et al, 1984;Holtz et al, 1992;Newman and Lowenstern, 2002;Papale et al, 2006) or tracking exsolution through fluid-mobile trace elements (Webster and Rebbert, 1998;Webster et al, 2020) provide a clear answer to the question of when volatile saturation occurs in a magmatic system's history; intermediate to silicic mushes in the mid to upper crust will become saturated with a MVP starting at low crystal volume…”

Section: Volatile Saturation and Timing Of Pegmatite Formationmentioning

confidence: 99%

The physical and chemical evolution of magmatic fluids in near-solidus silicic magma reservoirs: Implications for the formation of pegmatites

Troch

Huber

2022

American Mineralogist

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As ascending magmas undergo cooling and crystallization, water and fluid-mobile elements (e.g. Li, B, C, F, S, Cl) become increasingly enriched in the residual melt, until fluid saturation is reached. The consequential exsolution of a fluid phase dominated by H 2 O (magmatic volatile phase or MVP) is predicted to occur early in the evolution of long-lived crystal-rich "mushy" magma reservoirs, and can be simulated by tracking the chemical and physical evolution of these reservoirs in thermomechanical numerical models. Pegmatites are commonly interpreted as the products of crystallization of late-stage volatile-rich liquids sourced from granitic igneous bodies. However, little is known about the timing and mechanism of extraction of pegmatitic liquids from their source. In this study, we review findings from thermomechanical models on the physical and chemical evolution of melt and MVP in near-solidus magma reservoirs, and apply these to textural and chemical observations from pegmatites. As an example, we use a three-phase compaction model of a section of a mushy reservoir, and couple this to fluid-melt and mineral-melt partition coefficients of volatiles trace elements (Li, Cl, S, F, B). We track various physical parameters of melt, crystals and MVP, such as volume fractions, densities, velocities, as well as the content in the volatile trace elements mentioned above. The results suggest that typical pegmatite-like compositions (i.e. enriched in incompatible elements) require high crystallinities (>70-75 vol% crystals) in the magma reservoir, at which MVP is efficiently trapped in the crystal network. Fluid-mobile trace elements can become enriched beyond contents expected from closed-system equilibrium crystallization This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Chlorine and felsic magma evolution: Modeling the behavior of an under-appreciated volatile component

Cited by 23 publications

References 184 publications

The Systematics of Chlorine, Lithium, and Boron andδ³⁷Cl,δ⁷Li, and δ¹¹B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field

The Systematics of Chlorine, Lithium, and Boron andδ³⁷Cl,δ⁷Li, and δ¹¹B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field

Chlorine isotope ratios record magmatic brine assimilation during rhyolite genesis

The physical and chemical evolution of magmatic fluids in near-solidus silicic magma reservoirs: Implications for the formation of pegmatites

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Chlorine and felsic magma evolution: Modeling the behavior of an under-appreciated volatile component

Cited by 23 publications

References 184 publications

The Systematics of Chlorine, Lithium, and Boron andδ37Cl,δ7Li, and δ11B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field

The Systematics of Chlorine, Lithium, and Boron andδ37Cl,δ7Li, and δ11B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field

Chlorine isotope ratios record magmatic brine assimilation during rhyolite genesis

The physical and chemical evolution of magmatic fluids in near-solidus silicic magma reservoirs: Implications for the formation of pegmatites

Contact Info

Product

Resources

About

The Systematics of Chlorine, Lithium, and Boron andδ³⁷Cl,δ⁷Li, and δ¹¹B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field

The Systematics of Chlorine, Lithium, and Boron andδ³⁷Cl,δ⁷Li, and δ¹¹B in the Hydrothermal System of the Yellowstone Plateau Volcanic Field